Abstract

We study the decay of multiple quantum (MQ) NMR coherences in systems with the large number of equivalent spins. As being created on the preparation period of the MQ NMRexperiment, they decay due to the dipole–dipole interactions (DDI) on the evolution period of this experiment. It is shown that the relaxation time decreases with the increase in MQ coherence order (according to the known results) and in the number of spins. We also consider the modified preparation period of the MQ NMRexperiment [G. A. Alvarez and D. Suter, Phys. Rev. Lett.104, 230403 (2010)] concatenating the short evolution periods under the secular DDI Hamiltonian (the perturbation) with the evolution period under the nonsecular averaged two-spin/two-quantum Hamiltonian. The influence of the perturbation on the decoherence rate is investigated for the systems consisting of 200–600 equivalent spins.

All numerical simulations have been performed using the resources of the Joint Supercomputer Center (JSCC) of the Russian Academy of Sciences. Authors thank the anonymous referee for the valuable remarks. The work was supported by the Program of the Presidium of Russian Academy of Sciences No. 21 “Foundations of fundamental investigations of nanotechnologies and nanomaterials.”

Article outline:I. INTRODUCTIONII. THE MQ NMREXPERIMENTS IN A SYSTEM OF EQUIVALENT SPINSA. Preparation periodB. Evolution periodC. Mixing periodIII. THE DECAY OF MQ NMRCOHERENCE INTENSITIES CAUSED BY THE SECULAR DDIA. The decay of MQ NMR coherences in MQ NMRexperiments of Ref. 51. The numerical simulationsB. The decay of MQ NMR coherences in MQ NMRexperiments with the modified preparation period1. The numerical simulationsIV. THE CONSERVATION LAW IN THE MODEL OF THE DIPOLAR RELAXATION OF MQ NMR COHERENCESV. CONCLUSIONS